Recent high resolution images of spiral galaxies show wide varieties of features including nuclear spirals in the central parts .
Some of the galaxies show grand-design nuclear spirals .
The morphology of grand-design spirals can be further divided by the openness of the arms : tightly wound ones with winding angle of around 3 \pi radian and open spirals with winding angle of around \pi radian .
Based on hydrodynamical simulations , we have investigated the mechanism responsible for the openness of nuclear spirals .
Since the gas flow in the nuclear region is mainly governed by the central mass concentration near the nuclei and the sound speed of the gas , we have examined various models with different mass concentration represented by the mass of the central black hole and different sound speeds .
We found that the tightly wound spirals can be formed when the mass of the black hole is large enough to remove the inner-inner Lindblad resonances and sound speeds lie between 15 - 20 km/sec .
Thus , the presence of the tightly wound nuclear spiral could imply the presence of relatively massive black hole in the center .